1. Field of Invention
The present invention relates to a method and a system of controlling a series-parallel hybrid power system, in particularly, to a series-parallel coupling control method and system of a hybrid power system.
2. Related Art
A common hybrid power vehicle is to selectively operate under a parallel or series mode, i.e., selectively drive a vehicle to move in a parallel or series output mode. For the parallel output mode, the clutch is in a closed state and the engine and the motor output power in sync to drive the vehicle. For the series mode, the clutch is in an open state and the vehicle is only driven by the motor to move.
Relevant technology regarding hybrid power vehicle (wheel vehicle) can be found in U.S. Pat. No. 6,318,486 entitled “Hybrid Vehicle”, issued on Nov. 20, 2001, which discloses a series-parallel hybrid power wheel vehicle. The technology disclosed therein is in that, once the clutch has poor joining (sliding) or becomes too hot, the hybrid power system of the vehicle is actuated to be converted into the series mode (i.e., the clutch is open, and then the motor, instead of the engine, outputs power to drive the vehicle), so as not to deteriorate the driving characteristics of the vehicle due to the problems in the clutch.
U.S. Pat. No. 6,998,727, issued on Feb. 14, 2006, proposes methods of operating a parallel hybrid vehicle having an internal combustion engine and a secondary power source. U.S. Pat. No. 6,876,098, issued on Apr. 5, 2005, discloses methods of operating a series hybrid vehicle.
When switching from the series mode to the parallel mode, or from the parallel mode to the series mode, the current hybrid power vehicle may suffer from sudden thrust (suddenly speed up) or a jerk (suddenly slow down by the power source) because of insufficient switching fluency. Sudden thrust is due to sudden change of the vehicle from one power source to two power sources, and jerk is due to sudden change of the vehicle from two power sources to one power source. Either sudden thrust or jerk will cause pitching movement of the vehicle at the instant of mode switching, thereby greatly reducing comfortability of drivers or passengers.